Heretofore, europium activated rare earth element oxysulfide (which will hereinafter often be referred to as "Ln.sub.2 O.sub.2 S:Eu" including, for example, "Y.sub.2 O.sub.2 S:EU" for europium activated yttrium oxysulfide) phosphors have been employed as a red emitting phosphor for a color picture tube, since these phosphors each have a high emission efficiency, are capable of controlling the color tone and are chemically stable so as to be suitable for use in a slurry coating method.
On the other hand, as one requisite for improving the properties of a color tube, it is required to enlarge the scope of color reproduction and develop therefor a red emitting phosphor having a deep chromaticity, This phosphor can readily be obtained by increasing the europium concentration, but increase of the brightness thereof is not always sufficiently obtained. In particular, as a countermeasure for the latest largesizing of a television or for a "High Definition TV" it has strongly been desired improve the brightness, but the situation does not satisfy the countermeasure. That is, the emission efficiency of the Ln.sub.2 O.sub.2 S:Eu phosphor itself has exhaustedly been improved nearly to the saturation state.
As is well known in the art, there are other red emitting phosphors, for example europium activated rare earth element oxide phosphors, europium activated rare earth element vanadate phosphors, silver activated zinc cadmium sulfide phosphors, manganese activated zinc phosphate phosphors and the like. However, any of these phophors do not satisfy the above described color reproduction and brightness. Thus, there has been proposed a method comprising using a face plate containing neodymium or other elements, a method comprising providing a face plate with a special color filter on the surface thereof, a method comprising adding a specified pigment to a fluorescent film and the like. These methods consist of adding a filtering function to a specified wavelength of emitting colors of a phosphor to limit the transmittance of the light with the specified wavelength and thus enlarging the scope of color production. In any case, the effective brightness decreases.
It is an object of the present invention to provide a color picture tube, which has a fluorescent film of a red emission constituent exhibiting a red emission with a deep color tone and is excellent in emission brightness, and whereby the above described problems can be solved.
It is another object of the present invention to provide a cathode ray tube for color television, whereby the chemical stability of an europium activated rare earth element oxide (which will hereinafter often be referred to as Ln.sub.2 O.sub.3 :Eu) phosphor, as a red emission phosphor, is improved and application of a slurry coating method to the above described fluorescent film of a red emission constituent is rendered possible.
It is a further object of the present invention to provide a cathode ray tube for color television, which is excellent in emission brightness, color reproduction and beam current balance, by choosing emission colors in the specified range for those of the above described red emission constituent fluorescent film, a green emission constituent fluorescent membrane and a blue emission constituent fluorescent film.